In the prior art electronic spanner, the spanner is installed with an electronic device and stain gauge. The electronic device has the effect of measuring the resistance variation of the stain gauge so as to get the twisting force applied to the spanner from the variation of the resistance of the stain gauge. Thereby the user can know whether the screw means is too tight so as to destroy the screw means or too loose to be tightened to an object.
However the cost of the prior art electronic spanner is too high to be acceptable. Thereby the display head is fixed to the spanner body. The display head cannot rotate with respect to the spanner body. The sensing head is non-replaceable. Thereby as it is desired to use different hand tools, the stain gauge cannot be replaced. Thereby the user must buy a new hand tool with the stain gauge.